Advance movie screenings for critics take place in darkened rooms several times a week. Their locations are generally closed to the public - it's probably easier to infiltrate a Freemason initiation ceremony. And reviews are embargoed by film studios until opening day.

The prescreenings are part of a symbiotic relationship between writers and studios that has lasted for almost a century. By showing its latest fare to reviewers, the industry stands to benefit from publicity, especially if critics offer the sort of kudos that can be blurbed for TV and print ads. For critics, the previews are essential if their critiques are to coincide with a film's opening.

Lately, though, that relationship has been fraying. This year, more and more films have been withheld from the press prior to opening day - the latest being "Silent Hill," a horror film debuting Friday - perhaps because studios have calculated that they can attract audiences regardless of whether the films have been reviewed beforehand. While it's not unprecedented for film companies to nix such previews, the recent trend underscores the extent to which the industry's changing business model relies less on critics for promoting certain types of mainstream fare.

"I've talked with the advertising guys at studios about it," says Peter Bart, lead columnist at Variety magazine. "The media world is changing, and the people they want to reach are the kids who are looking at MySpace.com and exchanging instant messages about pictures aimed at them. Conventional critics don't matter."

For the most part, the movies not prescreened tend to be youth-oriented: Horror films featuring inappropriate uses of chainsaws and slapstick comedies featuring inappropriate uses of that guy from "Napoleon Dynamite." There have been 12 such movies so far this year, compared with three during the same period last year and two the year before. Some of the films - "The Benchwarmers" ($20 million opening weekend), "Underworld Evolution" ($27 million), and "Madea's Family Reunion" ($30 million) - scored impressive box-office numbers during opening weekend. Others, such as "Doogal" ($3.6 million) and "Grandma's Boy" ($3 million) will soon be found next to that dusty DVD of "Battlefield Earth" in video-store bargain bins - probably within a few weeks.